1. Field of the Invention
The invention relates to spray cans for dispensing paint and, more particularly, to a dispenser in which a pressurized reactive component such as a dihydroxyl curing agent is stored in one can, and solvent, isocyanate catalyst and propellant are stored in another can. The components of the two cans are maintained separately until needed, at which time a seal between them is broken by a valve within a threaded coupling.
2. Description of the Prior Art
Automotive paint spraying systems for small-scale restoration of the finish of older vehicles or to repair nicks and scratches have been known for many years. The familiar spray paint can is simply a rolled metal can filled with pressurized propellant and a previously cured thermoset paint or coating which has been pulverized into very small particulates and suspended in a solvent. After being sprayed onto the part surface, the solvent is allowed to evaporate, leaving a dry, hard paint layer.
While this is a convenient and inexpensive application method, the paint layer being applied does not approach the level of durability and protection of which the thermoset coating material is capable. This is because the thermoset particulates that make up the paint layer are only softened by the solvent and not actually dissolved. The resulting paint layer is thus made up of tiny overlapping paint chips. While they are stuck together sufficiently to give an apparently uniform surface, the surface is in fact discontinuous at a microscopic scale. The surface thus lacks integrity at the microscopic scale, limiting durability, and the residual porosity permits environmental agents to penetrate to the substrate.
To achieve a continuous thermoset paint surface, such as that applied by original equipment manufacturers, chemically reactive components must be applied so as to cure seamlessly on the part surface itself. Such familiar paints as epoxies, polyurethanes, and polyacrylamides generally require mixing a pigmented reactive constituent with a catalyst or curing agent which initiates the thermosetting reaction. The reacting mixture is then sprayed under pressure from a compressor onto the surface to be painted, where both chemical reaction and solvent evaporation take place.
While the paint layer so applied demonstrates superior durability and imparts improved weather and corrosion resistance to the substrate, this application mode has several limitations. Because the reaction takes place quickly, and generally runs to completion once begun, application of reactive systems often involves fairly rigorous storage precautions, careful application preparation, and solvent-intensive clean-up procedures. Moreover, the chemical reactants themselves often may only be purchased in bulk, at least relative to the amount of paint needed to repair the usual scratches and nicks a home do-it-yourselfer would be repainting. In addition, such multi-constituent paint application also requires mixing componentry such as a spray gun and a compressor, with their attendant cost of rental or purchase.
Several attempts have been made to match the convenience of a small spray can dispenser with the durability and protection of a reactive system. These systems generally involve linking separate, differentially pressurized canisters containing the reactive species by means of valves which permit the constituents to be mixed together just prior to application. Such an arrangement permits better coatings to be applied from more convenient, disposable dispensers.
Such systems include those described in U.S. Pat. No. 3,181,737 to Chaucer, U.S. Pat. No. 3,343,718 to Siegel et at., U.S. Pat. No. 3,698,453 to Morane et al., and U.S. Pat. No. 4,988,017 to Schrader et al. In these devices, a vessel containing fluid under higher pressure is coupled through one or more mechanically operated valves to a vessel under lower pressure. These mechanical valves generally include many components, some of which require close tolerances and detailed machining. Upon activating the valves, the higher pressure fluid is transferred into the lower pressure container, from which the mixture of the two fluids can be sprayed.
While these two-canister systems offer superior coating potential, they have relatively complicated coupling valves, which add unnecessary cost to the system. Somewhat simpler valves are disclosed in U.S. Pat. No. 3,556,171 to Gangwisch et al., U.S. Pat. No. 3,314,571 to Greenebaum, and U.S. Pat. No. 3,817,297 to King, each of which discloses a re-tillable aerosol system. These latter systems, however, do not provide for the mixing of multiple constituents. Instead, they are intended to provide storage quantities of perfume, for example, that can be used to replenish smaller dispenser canisters.
Desirably, an aerosol paint dispenser for home or shop use by the do-it-yourselfer should be compact to reflect the generally limited amount of paint needed for the ordinary use to which it is put. The dispenser also should allow the application of reactive constituents to provide a coating which is physically and chemically superior to those of common spray paints. Further, the dispenser should provide means of assuring that the constituents are kept separate from each other until needed for use. The dispenser package also should be sufficiently inexpensive and simple to use so that it will be purchased and used by as many consumers as possible.